/*
 * Copyright (c) 2003, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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 */

package java.util;

import java.security.*;

/**
 * A class that represents an immutable universally unique identifier (UUID).
 * A UUID represents a 128-bit value.
 *
 * <p> There exist different variants of these global identifiers.  The methods
 * of this class are for manipulating the Leach-Salz variant, although the
 * constructors allow the creation of any variant of UUID (described below).
 *
 * <p> The layout of a variant 2 (Leach-Salz) UUID is as follows:
 *
 * The most significant long consists of the following unsigned fields:
 * <pre>
 * 0xFFFFFFFF00000000 time_low
 * 0x00000000FFFF0000 time_mid
 * 0x000000000000F000 version
 * 0x0000000000000FFF time_hi
 * </pre>
 * The least significant long consists of the following unsigned fields:
 * <pre>
 * 0xC000000000000000 variant
 * 0x3FFF000000000000 clock_seq
 * 0x0000FFFFFFFFFFFF node
 * </pre>
 *
 * <p> The variant field contains a value which identifies the layout of the
 * {@code UUID}.  The bit layout described above is valid only for a {@code
 * UUID} with a variant value of 2, which indicates the Leach-Salz variant.
 *
 * <p> The version field holds a value that describes the type of this {@code
 * UUID}.  There are four different basic types of UUIDs: time-based, DCE
 * security, name-based, and randomly generated UUIDs.  These types have a
 * version value of 1, 2, 3 and 4, respectively.
 *
 * <p> For more information including algorithms used to create {@code UUID}s,
 * see <a href="http://www.ietf.org/rfc/rfc4122.txt"> <i>RFC&nbsp;4122: A
 * Universally Unique IDentifier (UUID) URN Namespace</i></a>, section 4.2
 * &quot;Algorithms for Creating a Time-Based UUID&quot;.
 *
 * @since 1.5
 */
public final class UUID implements java.io.Serializable, Comparable<UUID> {

  /**
   * Explicit serialVersionUID for interoperability.
   */
  private static final long serialVersionUID = -4856846361193249489L;

  /*
   * The most significant 64 bits of this UUID.
   *
   * @serial
   */
  private final long mostSigBits;

  /*
   * The least significant 64 bits of this UUID.
   *
   * @serial
   */
  private final long leastSigBits;

  /*
   * The random number generator used by this class to create random
   * based UUIDs. In a holder class to defer initialization until needed.
   */
  private static class Holder {

    static final SecureRandom numberGenerator = new SecureRandom();
  }

  // Constructors and Factories

  /*
   * Private constructor which uses a byte array to construct the new UUID.
   */
  private UUID(byte[] data) {
    long msb = 0;
    long lsb = 0;
    assert data.length == 16 : "data must be 16 bytes in length";
    for (int i = 0; i < 8; i++) {
      msb = (msb << 8) | (data[i] & 0xff);
    }
    for (int i = 8; i < 16; i++) {
      lsb = (lsb << 8) | (data[i] & 0xff);
    }
    this.mostSigBits = msb;
    this.leastSigBits = lsb;
  }

  /**
   * Constructs a new {@code UUID} using the specified data.  {@code
   * mostSigBits} is used for the most significant 64 bits of the {@code
   * UUID} and {@code leastSigBits} becomes the least significant 64 bits of
   * the {@code UUID}.
   *
   * @param mostSigBits The most significant bits of the {@code UUID}
   * @param leastSigBits The least significant bits of the {@code UUID}
   */
  public UUID(long mostSigBits, long leastSigBits) {
    this.mostSigBits = mostSigBits;
    this.leastSigBits = leastSigBits;
  }

  /**
   * Static factory to retrieve a type 4 (pseudo randomly generated) UUID.
   *
   * The {@code UUID} is generated using a cryptographically strong pseudo
   * random number generator.
   *
   * @return A randomly generated {@code UUID}
   */
  public static UUID randomUUID() {
    SecureRandom ng = Holder.numberGenerator;

    byte[] randomBytes = new byte[16];
    ng.nextBytes(randomBytes);
    randomBytes[6] &= 0x0f;  /* clear version        */
    randomBytes[6] |= 0x40;  /* set to version 4     */
    randomBytes[8] &= 0x3f;  /* clear variant        */
    randomBytes[8] |= 0x80;  /* set to IETF variant  */
    return new UUID(randomBytes);
  }

  /**
   * Static factory to retrieve a type 3 (name based) {@code UUID} based on
   * the specified byte array.
   *
   * @param name A byte array to be used to construct a {@code UUID}
   * @return A {@code UUID} generated from the specified array
   */
  public static UUID nameUUIDFromBytes(byte[] name) {
    MessageDigest md;
    try {
      md = MessageDigest.getInstance("MD5");
    } catch (NoSuchAlgorithmException nsae) {
      throw new InternalError("MD5 not supported", nsae);
    }
    byte[] md5Bytes = md.digest(name);
    md5Bytes[6] &= 0x0f;  /* clear version        */
    md5Bytes[6] |= 0x30;  /* set to version 3     */
    md5Bytes[8] &= 0x3f;  /* clear variant        */
    md5Bytes[8] |= 0x80;  /* set to IETF variant  */
    return new UUID(md5Bytes);
  }

  /**
   * Creates a {@code UUID} from the string standard representation as
   * described in the {@link #toString} method.
   *
   * @param name A string that specifies a {@code UUID}
   * @return A {@code UUID} with the specified value
   * @throws IllegalArgumentException If name does not conform to the string representation as
   * described in {@link #toString}
   */
  public static UUID fromString(String name) {
    String[] components = name.split("-");
    if (components.length != 5) {
      throw new IllegalArgumentException("Invalid UUID string: " + name);
    }
    for (int i = 0; i < 5; i++) {
      components[i] = "0x" + components[i];
    }

    long mostSigBits = Long.decode(components[0]).longValue();
    mostSigBits <<= 16;
    mostSigBits |= Long.decode(components[1]).longValue();
    mostSigBits <<= 16;
    mostSigBits |= Long.decode(components[2]).longValue();

    long leastSigBits = Long.decode(components[3]).longValue();
    leastSigBits <<= 48;
    leastSigBits |= Long.decode(components[4]).longValue();

    return new UUID(mostSigBits, leastSigBits);
  }

  // Field Accessor Methods

  /**
   * Returns the least significant 64 bits of this UUID's 128 bit value.
   *
   * @return The least significant 64 bits of this UUID's 128 bit value
   */
  public long getLeastSignificantBits() {
    return leastSigBits;
  }

  /**
   * Returns the most significant 64 bits of this UUID's 128 bit value.
   *
   * @return The most significant 64 bits of this UUID's 128 bit value
   */
  public long getMostSignificantBits() {
    return mostSigBits;
  }

  /**
   * The version number associated with this {@code UUID}.  The version
   * number describes how this {@code UUID} was generated.
   *
   * The version number has the following meaning:
   * <ul>
   * <li>1    Time-based UUID
   * <li>2    DCE security UUID
   * <li>3    Name-based UUID
   * <li>4    Randomly generated UUID
   * </ul>
   *
   * @return The version number of this {@code UUID}
   */
  public int version() {
    // Version is bits masked by 0x000000000000F000 in MS long
    return (int) ((mostSigBits >> 12) & 0x0f);
  }

  /**
   * The variant number associated with this {@code UUID}.  The variant
   * number describes the layout of the {@code UUID}.
   *
   * The variant number has the following meaning:
   * <ul>
   * <li>0    Reserved for NCS backward compatibility
   * <li>2    <a href="http://www.ietf.org/rfc/rfc4122.txt">IETF&nbsp;RFC&nbsp;4122</a>
   * (Leach-Salz), used by this class
   * <li>6    Reserved, Microsoft Corporation backward compatibility
   * <li>7    Reserved for future definition
   * </ul>
   *
   * @return The variant number of this {@code UUID}
   */
  public int variant() {
    // This field is composed of a varying number of bits.
    // 0    -    -    Reserved for NCS backward compatibility
    // 1    0    -    The IETF aka Leach-Salz variant (used by this class)
    // 1    1    0    Reserved, Microsoft backward compatibility
    // 1    1    1    Reserved for future definition.
    return (int) ((leastSigBits >>> (64 - (leastSigBits >>> 62)))
        & (leastSigBits >> 63));
  }

  /**
   * The timestamp value associated with this UUID.
   *
   * <p> The 60 bit timestamp value is constructed from the time_low,
   * time_mid, and time_hi fields of this {@code UUID}.  The resulting
   * timestamp is measured in 100-nanosecond units since midnight,
   * October 15, 1582 UTC.
   *
   * <p> The timestamp value is only meaningful in a time-based UUID, which
   * has version type 1.  If this {@code UUID} is not a time-based UUID then
   * this method throws UnsupportedOperationException.
   *
   * @return The timestamp of this {@code UUID}.
   * @throws UnsupportedOperationException If this UUID is not a version 1 UUID
   */
  public long timestamp() {
    if (version() != 1) {
      throw new UnsupportedOperationException("Not a time-based UUID");
    }

    return (mostSigBits & 0x0FFFL) << 48
        | ((mostSigBits >> 16) & 0x0FFFFL) << 32
        | mostSigBits >>> 32;
  }

  /**
   * The clock sequence value associated with this UUID.
   *
   * <p> The 14 bit clock sequence value is constructed from the clock
   * sequence field of this UUID.  The clock sequence field is used to
   * guarantee temporal uniqueness in a time-based UUID.
   *
   * <p> The {@code clockSequence} value is only meaningful in a time-based
   * UUID, which has version type 1.  If this UUID is not a time-based UUID
   * then this method throws UnsupportedOperationException.
   *
   * @return The clock sequence of this {@code UUID}
   * @throws UnsupportedOperationException If this UUID is not a version 1 UUID
   */
  public int clockSequence() {
    if (version() != 1) {
      throw new UnsupportedOperationException("Not a time-based UUID");
    }

    return (int) ((leastSigBits & 0x3FFF000000000000L) >>> 48);
  }

  /**
   * The node value associated with this UUID.
   *
   * <p> The 48 bit node value is constructed from the node field of this
   * UUID.  This field is intended to hold the IEEE 802 address of the machine
   * that generated this UUID to guarantee spatial uniqueness.
   *
   * <p> The node value is only meaningful in a time-based UUID, which has
   * version type 1.  If this UUID is not a time-based UUID then this method
   * throws UnsupportedOperationException.
   *
   * @return The node value of this {@code UUID}
   * @throws UnsupportedOperationException If this UUID is not a version 1 UUID
   */
  public long node() {
    if (version() != 1) {
      throw new UnsupportedOperationException("Not a time-based UUID");
    }

    return leastSigBits & 0x0000FFFFFFFFFFFFL;
  }

  // Object Inherited Methods

  /**
   * Returns a {@code String} object representing this {@code UUID}.
   *
   * <p> The UUID string representation is as described by this BNF:
   * <blockquote><pre>
   * {@code
   * UUID                   = <time_low> "-" <time_mid> "-"
   *                          <time_high_and_version> "-"
   *                          <variant_and_sequence> "-"
   *                          <node>
   * time_low               = 4*<hexOctet>
   * time_mid               = 2*<hexOctet>
   * time_high_and_version  = 2*<hexOctet>
   * variant_and_sequence   = 2*<hexOctet>
   * node                   = 6*<hexOctet>
   * hexOctet               = <hexDigit><hexDigit>
   * hexDigit               =
   *       "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"
   *       | "a" | "b" | "c" | "d" | "e" | "f"
   *       | "A" | "B" | "C" | "D" | "E" | "F"
   * }</pre></blockquote>
   *
   * @return A string representation of this {@code UUID}
   */
  public String toString() {
    return (digits(mostSigBits >> 32, 8) + "-" +
        digits(mostSigBits >> 16, 4) + "-" +
        digits(mostSigBits, 4) + "-" +
        digits(leastSigBits >> 48, 4) + "-" +
        digits(leastSigBits, 12));
  }

  /**
   * Returns val represented by the specified number of hex digits.
   */
  private static String digits(long val, int digits) {
    long hi = 1L << (digits * 4);
    return Long.toHexString(hi | (val & (hi - 1))).substring(1);
  }

  /**
   * Returns a hash code for this {@code UUID}.
   *
   * @return A hash code value for this {@code UUID}
   */
  public int hashCode() {
    long hilo = mostSigBits ^ leastSigBits;
    return ((int) (hilo >> 32)) ^ (int) hilo;
  }

  /**
   * Compares this object to the specified object.  The result is {@code
   * true} if and only if the argument is not {@code null}, is a {@code UUID}
   * object, has the same variant, and contains the same value, bit for bit,
   * as this {@code UUID}.
   *
   * @param obj The object to be compared
   * @return {@code true} if the objects are the same; {@code false} otherwise
   */
  public boolean equals(Object obj) {
    if ((null == obj) || (obj.getClass() != UUID.class)) {
      return false;
    }
    UUID id = (UUID) obj;
    return (mostSigBits == id.mostSigBits &&
        leastSigBits == id.leastSigBits);
  }

  // Comparison Operations

  /**
   * Compares this UUID with the specified UUID.
   *
   * <p> The first of two UUIDs is greater than the second if the most
   * significant field in which the UUIDs differ is greater for the first
   * UUID.
   *
   * @param val {@code UUID} to which this {@code UUID} is to be compared
   * @return -1, 0 or 1 as this {@code UUID} is less than, equal to, or greater than {@code val}
   */
  public int compareTo(UUID val) {
    // The ordering is intentionally set up so that the UUIDs
    // can simply be numerically compared as two numbers
    return (this.mostSigBits < val.mostSigBits ? -1 :
        (this.mostSigBits > val.mostSigBits ? 1 :
            (this.leastSigBits < val.leastSigBits ? -1 :
                (this.leastSigBits > val.leastSigBits ? 1 :
                    0))));
  }
}
